Reversible retention of synchronized HeLa cells in G2 of the mammalian cell cycle

The rate of progression of cycling HeLa cells from G2 into mitosis is greatly reduced by the amino acid analogue, p-fluorophenylalanine, but a small percentage of cells continually escapes into mitosis. Most of a presynchronized population can be held for several h in G2, thereby facilitating analyses of cells at this late stage of the cell cycle. They are reversed from the block by the addition of phenylalanine and resume progression within about 1 h with predictable kinetics but without a significantly enhanced synchrony. The mechanism of action of the analogue is consistent with the hypothesis that synthesis of false proteins interferes with the correct assembly of division-relevant structures.